Activation of Host Immune Cells by Probiotic-Derived Extracellular Vesicles via TLR2-Mediated Signaling Pathways

Since probiotic-derived extracellular vesicles (EVs) are capable of activating innate immunity, they are expected to be useful as novel adjuvants. To elucidate the mechanisms underlying the immunostimulatory effects of EVs released from probiotic cells, we newly investigated the role of Toll-like receptor 2 (TLR2) and immune cell downstream signaling in the generation of proinflammatory cytokines. Isolated Bifidobacterium- and Lactobacillus-derived EVs expressed peptidoglycan, one of the major pathogen-associated molecular patterns. EVs particle diameter were approximately 110–120 nm with a negative-zeta potential. The generation of proinflammatory cytokines (tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in TLR2-expressing mouse macrophage-like RAW264.7 cells and mouse dendritic DC2.4 cells treated with Bifidobacterium- and Lactobacillus-derived EVs decreased after the addition of T2.5, a TLR2 inhibitory antibody. Furthermore, we showed that the signaling pathways of c-Jun-NH2-terminal kinase (JNK)/mitogen-activated protein kinases (MAPK) and nuclear factor-kappaB (NF-κB) were also involved in the production of proinflammatory cytokines from EV-treated immune cells. These results provide valuable information for understanding of the host biological function induced by probiotic-derived EVs, which is helpful for developing an EV-based immunotherapeutic system.